This invention relates to the storage of wheeled trailer frames of the type used to haul cargo containers over the road.
Wheeled trailer frames, often referred to as "chassis," must be stored at ship or rail loading sites. They may, of course, be stored in their normal horizontal position by lowering their front vertically adjustable jacks or .music-flat.landing gear." Such storage consumes a large amount of critical space at a loading site. It also leaves the chassis vulnerable to unauthorized removal.
Attempts have been made to solve the problems of chassis storage by means of systems and apparatus for swinging chassis into a vertical position and retrievably storing them in specially designed storage racks. Apparatus by which a tractor or forklift truck can be used to flip a chassis into vertical position and transport it to a storage facility are described in Riley U.S. Pat. No. 4,583,902, entitled Method and System for Storing Wheeled Frames of Detachable Cargo Container Type Trailers, and Perrott U.S. Pat. No. 4,437,807, entitled Wheeled Trailer Frame Carrying Unit Attachment for Lift Truck. Storage racks for vertically oriented chassis are described in Riley U.S. Pat. No. 4,583,902 and in Corbett et al. U.S. Pat. No. 4,549,663, entitled Storage System for Trailer Frames. While the apparatus and systems disclosed in the above Riley, Perrott and Corbett et al. patents offer improvements over individual chassis storage, they suffer from serious drawbacks and disadvantages.
Taking first the chassis flipping method and apparatus, Perrott U.S. Pat. No. 4,437,807 discloses a carriage 30 which is mounted on the mast of a forklift truck in place of the fork. This is a rather permanent attachment, which is an immediate drawback. The carriage supports an elongated boom 32 of I-beams 34, which in turn supports a movable carriage carrying hydraulically operated horizontal clamps and vertical clamps to engage the side rails of the chassis. The boom also has carrier support pads 98 to engage the rear bolster of the chassis. The combined weight of the flipping apparatus and the chassis results in a large moment about the mast. The forklift size and capacity, and the mast itself must be capable of withstanding the large moment at the start of flipping, and a large counterweight on the forklift generally will be required. In addition, experience with flipping apparatus of the type described has resulted in a high incidence of damage to tail lights, stop lights and marker lights positioned along the rear bolster of the chassis.
To engage a chassis the flipping truck approaches it from the rear. As it does so, the boom must align with the longitudinal centerline of the chassis. According to Perrott U.S. Pat. No. 4,437,807, either the lift truck must be capable of moving its mast laterally (there are available attachments for lift trucks known as "side shifters"), or else the lift truck operator must reposition his vehicle to line up with the longitudinal centerline of the chassis. Obviously, expense is involved no matter which course is followed. Riley U.S. Pat. No. 4,583,902 discloses a side shifter arrangement for a mounting frame attachment for a tractor, that shifter comprising a transversely movable carriage which can be shifted by a pair of hydraulic cylinders 72. This increases the cost and complexity of the flipping apparatus and adds weight to the forward section of the boom.
Turning to the vertical storage rack, additional drawbacks are seen. Riley discloses a storage rack arrangement having a central channel for storing a row of vertically oriented chassis, and side channels for retractable gate mechanisms to hold each chassis. The rack is an open beam structure, roughly U-shaped, with vertical support beams which appear to be about half the length of a chassis--and chassis are typically 23 feet and 40 feet in length. Corbett et al. U.S. Pat. No. 4,549,663 discloses a tree-like storage rack having a central open-beam support structure from which retractable arms extend outwardly on both sides to support vertically oriented chassis. The Corbett et al. structure appears to be about three quarters as high as a chassis is long, or about 18 feet high. The structure is said to be supported by suitable anchoring means such as base members 12' and 14'.
A commercial rack of the Corbett et al. type has retractable arms located approximately 17 feet above ground level. The arrangement has serious drawbacks. For example, to withstand the moment applied to the arms, the rack is heavy. A rack which can hold 18 chassis weights about 17,000 lbs., or nearly 1000 lbs. per chassis. The rack must be anchored to the ground by means of large subsurface foundations or above-ground counterweights. If designed to withstand winds of 80 mph impinging on a fully loaded rack from the side, each vertical post must withstand a moment of 300,000 ft-lbs.
The racks of both Riley and Corbett et al. are rather complex in design, with retractable gates or arms. They must be fabricated in a variety of different-sized parts, including certain heavy pieces, and erected on site. The Corbett et al. rack additionally requires a previously prepared subsurface foundation, as described above. The racks are complex, heavy, and expensive, and are not easy to assemble or relocate. On the other hand, vertical storage racks of Corbett et al. do significantly save ground space for storing chassis as compared to a parking lot, reducing the amount of land consumed by about 75-80% (depending on arrangement) for 23-ft. chassis and by 85-89% for 40-ft. chassis. It will be readily appreciated why there is greater savings through vertical storage of longer chassis as compared to shorter chassis.